Photos.com/Thinkstock(SAN FRANCISCO) -- A website designer, who claims a California gym chain refused to pay his invoices for work completed, took the unusual step of hacking into and commandeering the client’s websites.

Fitness SF, a chain of California gyms, allegedly failed to pay Frank Jonen, who says he is a freelance web designer, photographer and writer/director in Idstein, Germany, according to his Facebook page. He then broke into the Fitness SF web site and reposted the home page with his rant on the company’s alleged failure to pay on time.

Instead of information about say, Pilates and hot yoga, consumers who log on to the site were greeted with this as of Friday: “Dear Fitness Customer. Fitness SF preferred to ignore our invoices instead of paying them. As a result this website is no longer operational.” Links to Fitness SF locations in Oakland, Marin, and SOMA and the Castro areas in San Francisco, also redirect to this message.

Jonen seems to see himself as somewhat of an activist, fighting for the rights of independent contractors everywhere. “I am also writing this on behalf of the tens of thousands of freelancers and small businesses out there facing larger corporations who can afford to starve them out. …An injury to one is an injury to all of us. We need to make a stand against crooks like this.”

The screed ends with a plea for consumers to cancel gym memberships, Tweet, or post on their Facebook pages in solidarity with him.

According to Ad Age (the piece originally appeared on the Denver Egotist), Jonen had intimated on Twitter that he might do something rash.

“I bet these bastards still think I won’t fight back and let them get away with betraying me and escaping payment,” he tweeted to his more than 1,500 followers. Another Tweet pointed people to the revamped web site: “They thought paying invoices was ‘optional’. They ignored all reminders. Let’s see if they’ll ignore this: http://fitnesssf.com/” he wrote.

In an email to ABC News, director of operations Don Dickerson of Fitness SF, said that its domain name had been “hacked and stolen.” He added that Jonen had been paid $5,000 on May 16, 2012 to develop a functional website for the brand, promising a 10-week delivery date.

“He missed numerous deadlines including our brand launch in September,” said Dickerson. “In December, he voluntarily passed the incomplete and non functioning website to our new design firm. Now, Frank is attempting to portray himself as the victim when truly the victim is Fitness SF.”